Hello

In general formalin and high temperatures with different solvents to put specimens in paraffin causes DNA degradation . However, there are many experiences in this field and the results were stunning .

you can do that provided that consider the age of the block and choose the best technique & kit for your sample .There are multitude of techniques (real time PCR , qPCR, Microarray, Western-Blot,...) and need to have the structural/morphological information of paraffin-embedded . 

We can help you best if Identified the type of cancer tissue & analysis you use in your studies

find attachment here , will help you

Good luck in your experience

http://genome.cshlp.org/content/3/6/S113.full.pdf+html

http://www.biomedcentral.com/content/pdf/1756-0500-3-239.pdf

http://www.sigmaaldrich.com/life-science/molecular-biology/dna-and-rna-purification/xna-tissue-pcr-protocol.html

http://www.ncbi.nlm.nih.gov/pubmed/1842921

http://www.mobio.com/blog/2012/07/20/formalin-fixed-paraffin-embedded-tissue-dna-isolation-the-basics/

http://jhc.sagepub.com/content/50/8/1005.full

http://scholarsresearchlibrary.com/ABR-vol3-iss7/ABR-2012-3-7-3174-3177.pdf

http://www.ncbi.nlm.nih.gov/pubmed/22237525